1. Field of the Invention
This invention relates to a joint structure for power transmitting member and a method for producing the joint structure for power transmitting member. More particularly, the present invention relates to a joint structure for propeller shaft for vehicle and method for producing the joint structure for propeller shaft for vehicle.
2. Description of the Related Art
It is known that there is a great demand for weight reduction in many fields, especially automobiles, from the viewpoint of fuel economy, environmental protection, etc. As a means for achieving this, use of propeller shafts formed of FRP (fiber-reinforced plastics) is being considered, and some of such propeller shafts have already been put into practical use. Such a propeller shaft has a tube that is made of FRP, and a metal joint that is joined to the end of the tube.
One example of a power transmitting member is the propeller shaft for a vehicle. The propeller shaft for a vehicle is disclosed in, for example, Japan Patent Publication (koukai) No. 2001-65538 (incorporated herein by reference). According to that publication, as shown in FIG. 11 of the pre-grant application, the propeller shaft includes an FRP tube 1 and universal joints 2, 3 which are joined to both ends 1a, 1b of the tube 1. A transmission torque generated from an engine (not shown) is transmitted to the following elements in order: a transmission (not shown), the universal joint 2, the tube 1, the universal joint 3, a differential gear (not shown), and a rear wheel (not shown).
The tube 1 comprises a main layer 1c and sub layers 4, 4. The main layer Ic has reinforcing fibers helically wound extending over the length thereof. The sub layers 4, 4 are formed at the ends of the main layer 1c so as to be integral with and internal to the main layer 1c and including hooped reinforcing fibers. The universal joints 2, 3 comprise input axis yokes 5, 5 and output axis yokes 6, 6. Each of the input axis yoke and the output axis yoke are joined together at yoke portions 7, 7. The output axis yokes have fitting portions 8, 8. Each of the fitting portions 8, 8 is joined to the ends 1a, 1b of the tube 1 by press fitting.
As shown in FIGS. 9 and 10 of the pre-grant application, the fitting portion 8 has a sealing portion 8a, a flange portion 9, and ajoint portion 10. The sealing portion 8a has a uniform outer diameter. The flange portion 9 is integrally molded with the fitting portion 8. When a load that is bigger than the prescribed value in an axial direction to the axis of the propeller shaft, is applied to the propeller shaft, the flange portion 9 causes the main layer 1c and the sub layer 4 to be separated from each other. This enables an energy absorbing effect to be realized due to the crashable body structure. The joint portion 10 has a serration surface. When the fitting portion 8 is joined to the end of the tube 1 by press fitting, a fastening structure between the tube 1 and the fitting portion 8 is obtained by engaging of the serration surface of the joint portion 10.
Next, a way to join each of the ends 1a, 1b and the fitting portions 8, 8 as shown in FIG. 11 will be described. As shown in FIGS. 9 and 10, first, a liquid packing compound 11 is applied to an edge of the joint portion 10, so as to surround the joint portion 10. Then, the tube 1 is forced into the joint portion 10 of the fitting portion 8 with press fitting until an end surface of the tube 1 almost strikes the flange portion 9. Thereby, the fastening structure between the tube 1 and the fitting portion 8 is obtained with press fitting. In addition, clearances between an inside of the tube 1 and an outer surface of the fitting portion 8, and between the end surface of the tube 1 and the flange portion 9 are filled with the liquid packing compound 11. In effect, the clearances are sealed by the liquid packing compound 11.
When the fitting portion 8 is joined to the end of the tube 1, the liquid packing compound 11 is spread between the inside of the tube 1 and the outer surface of the fitting portion 8. The liquid packing compound 11 is extended into the flange portion 9. However, in this structure for the power transmitting member, the sealing portion 8a has a uniform outer diameter, and the tube 1 has a uniform inner diameter, i.e., a clearance between the outer surface of the sealing portion 8a and the inside of the tube 1 has a uniform width in an axial direction of the axis of the tube 1. Therefore, a pressure force, which acts between the inside of the tube 1 and the outer surface of the fitting portion 8, is averaged around the edge of the inside of the tube 1. As a result, it is hard to fill to a corner 12, which defined between the flange portion 9 and the sealing portion 8a, entirely with the liquid packing compound 11.
Therefore, a failed portion C, in which the liquid packing compound does not adequately fill, may appear. In this case, airtightness between the tube 1 and fitting portion 8 by the liquid packing compound can not be retained. The airtightness degrades with the passage of time. As a result, the tube 1 and the fitting portion 8 may be separated from each other by exfoliation, i.e., the performance of the seal between the tube 1 and the fitting portion 8 may degrade.